This invention relates to coaxial connectors, and more particularly to coaxial connectors exhibiting relatively low mating and de-mating force requirements and transmission stability under severe environmental conditions.
Modern antenna design makes increasing use of broadside array antennas, in which a plurality of elemental antennas are arrayed to define a radiating aperture larger than that of a single elemental antenna, with the principal direction of radiation generally orthogonal to the plane of the array. Such array antennas have advantages by comparison with other types of antennas, as for example by virtue of being physically planar and broadside to the direction of radiation. When fitted with controllable phasing elements, the antenna beam or beams of such an array can be scanned without the need for motion of the array antenna as a whole. An array antenna is normally associated with a xe2x80x9cbeamformer,xe2x80x9d which specifies or controls the division of the signals to be transmitted among the antenna elements of the array, andor which specifies or controls the combination of signals received by the elements of the array to form the received signal. Such a beamformer has a finite loss, which directly contributes toward the noise figure of a receiver in a reception mode, and which attenuates the signal to be transmitted in a transmission mode.
The losses attributable to a beamformer can be ameliorated by associating each element or subarray of elements of an array antenna with an amplifier. In a reception mode, the signals received by each antenna element or subarray of antenna elements is amplified by a low-noise amplifier before being attenuated by the beamformer, so that the noise figure of the antenna-plus-receiver-plus beamformer arrangement is superior to that of an antenna-plus-beamformer-plus-low-noise amplifier. In a transmission mode of operation, associating each antenna element or subarray of antenna elements with a power amplifier allows the full power of each amplifier to be broadcast, rather than suffering the losses of the beamformer.
When array antennas are used, certain practical problems arise which relate to the making of connections. In two-dimensional arrays the beamforming is often configured by row and column combiners that are oriented normal to each other and normal to the aperture plane. The spacing between connectors in each row and the spacing between rows is generally equivalent to the spacing between the radiators in the array, which is inversely proportional to the operating frequency. Therefore, for high-frequency applications with small connector-to-connector spacing along the combiner boards, special connectors are needed to fit within the space constraints, because it is not possible to physically access individual connections, and the making of blind connections requires tight tolerances. It is in this row/column combining that the invention has been found to be most advantageous. It has been found that the metal spring contacts of conventional coaxial connectors tend to lose spring with time, especially in the presence of multiple cycles of mating and de-mating. Also, corrosion or equivalent degradation occurs, even in a space environment, which tends to affect the coupling. Variations in the magnitude andor phase of the coupling of connectors in the feed paths of elements of antenna arrays has been found to be a significant problem, because testing of such antennas and preparation for launch into space in the case of satellite antennas involves repeated mating and de-mating cycles. The mating involves making multiple simultaneous blind connections in the presence of axial and radial misalignments attributable to unavoidable mechanical tolerances. If the connectors themselves change coupling during the course of the various tests, it is difficult to separate problems in the antenna array and the associated amplifiers and phase shifters from problems in the connectors.
Improved connectors are desired.
A coaxial choke connector according to an aspect of the invention is for use with a coaxial transmission line having a characteristic impedance defined by an exterior first diameter of an inner conductor and an interior second diameter of an outer conductor, or at least a transmission line having a characteristic impedance characterizable by an exterior diameter of an inner conductor and an interior diameter of an outer conductor if it were coaxial. The coaxial choke connector includes a male portion and a female portion. The male portion of the coaxial choke connector includes an electrically conductive center choke conductor defining a proximal end and a distal end, and an electrically conductive outer choke conductor also defining a proximal end and a distal end. The proximal end of the center choke conductor is coupled to the inner conductor of the coaxial transmission line, and the proximal end of the outer choke conductor is coupled to the outer conductor of the coaxial transmission line. The center choke conductor of the male portion of the coaxial choke connector has a first length, a circular cross-section centered on a longitudinal axis, and a third diameter less than the first diameter. The outer choke conductor of the male portion of the coaxial choke connector has an inner fourth diameter which defines a circular cross-section centered on the axis and which is larger than the second diameter. The center choke conductor of the male portion has a layer of solid dielectric on the outer surface thereof, so that the center choke conductor with the layer of solid dielectric thereon has a fifth diameter smaller than the first diameter.
The female portion of the coaxial choke connector includes an electrically conductive center choke conductor and an electrically conductive outer choke conductor. The inner choke conductor of the female portion of the coaxial choke connector defines a closed-end axial bore with respect to the longitudinal axis, and the axial bore has a second length and a sixth diameter larger than the fifth diameter. In a preferred embodiment, the center choke conductor of the female portion has an outer diameter equal to the first diameter. The outer choke conductor of the female portion has an inner diameter equal to the second diameter, and an outer diameter coated with a solid dielectric material, so that the overall outer diameter of the outer choke conductor of the female portion, together with the solid dielectric material, has a seventh diameter, smaller than the fourth diameter. The coaxial choke connector also includes a stop arrangement associated with the male and female portions of the coaxial choke connector, for allowing the male and female portions to mate, but without allowing galvanic contact between (a) the distal end of the center choke conductor of the male portion and the closed end of the axial bore of the center choke conductor of the female portion and (b) the outer choke conductors of the male and female portions of the coaxial choke connector.
In a particularly advantageous embodiment of the coaxial choke connector, at least one of (a) the distal end of the center choke conductor of the male portion is tapered to a diameter smaller than the third diameter and (b) the distal end of the center choke conductor of the female portion is tapered to a thickness less than that existing over a portion of the center choke conductor remote from said distal end. In yet a further embodiment, the distal end of the center choke conductor of the male portion extends beyond the plane of the distal end of the outer choke conductor of the male portion, for enhancing the ability to mate the male and female portions.
The coaxial choke connector may be used with any unbalanced transmission line having a characteristic impedance near, or preferably equal to, that of the coaxial choke connector. Such a transmission line might be stripline or microstrip.